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Python | Rearrange Positive and Negative Elements
  • Last Updated : 05 Sep, 2019

Sometimes, while working with Python lists, we can have a problem in which we need to perform a sort in list. There are many variations of sorting that might be required to perform. Once such variation can be to sort elements of list, but keeping in mind, positive elements appear before negative elements. Let’s discuss a way in which this task can be performed.

Method : Using sorted() + lambda
This task can be performed using combination of above functions. In this, the logic we apply is computing inverse and negative of each number and then perform the sort using sorted(). The inversion makes sure that larger magnitude elements occur at middle and smaller at ends ( hill arrangement ) and negative takes care of making positives occur before negatives.

# Python3 code to demonstrate working of
# Sort while keeping Positive elements before negatives
# using sorted() + lambda
# initialize list
test_list = [4, -8, -6, 3, -5, 8, 10, 5, -19]
# printing original list
print("The original list is : " + str(test_list))
# Sort while keeping Positive elements before negatives
# using sorted() + lambda
res = sorted(test_list, key = lambda i: 0 if i == 0 else -1 / i)
# printing result
print("Result after performing sort operation : " + str(res))
Output :
The original list is : [4, -8, -6, 3, -5, 8, 10, 5, -19]
Result after performing sort operation : [3, 4, 5, 8, 10, -19, -8, -6, -5]

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